ACI 318 Appendix C Load Combinations

[JennyNakamura]

Does anybody ever use the load combos in ACI App C for strength design? I never give them a second thought, but today while working on a footing design I used Enercalc (an older version) to check my hand calcs and the output showed that the program uses App C. Then I pulled out an old college concrete design textbook (Nilson) and in the worked example I looked at he also used App C, though it wasn't stated -- I could just tell from the setup of the equations and the load factors.

When are we supposed to use App C instead of IBC/ASCE 7, and where can I find it in writing?

Thanks...

 

[DST148]

For design of concrete elements only, you have an option of using either load combinations and strength reduction factors given in Chapter 9 or load combinations and strength reduction factors given in Appendix C. The load combinations and strength reduction factors in Appendix C are similar to ACI 318 -99 and earlier versions of the code (legacy concrete codes) but modified to suit current building code lateral forces, e.g. earthquake forces at strength level, directionality factor for wind etc. Concrete designs either by Chapter 9 or Appendix C are comparable and acceptable. The load combinations and strength reduction factors must be consistent.
Also see ACI 318-05, Commentary R9.1, RC.1, and RC.2 for detailed info.

 

[Hokie93]

I suspect Enercalc simply didn't want to expend the effort to update that particular version of their software when the "new" load combinations were introduced (in ACI 318-02) so they used the equations in Appendix C, which is legitimate. The 14th edition of the Nilson concrete textbook (now by Nilson, Darwin, and Dolan) uses Chapter 9 load cominations and phi factors for footing design.